Semi-IPN polyurethane/polyurea protective films

ABSTRACT

Briefly, the present disclosure provides a film, tape or outer layer of a composite part comprising: a) at least one layer comprising a crosslinked polymer selected from the group consisting of crosslinked polyurethane, crosslinked polyurea, and crosslinked mixed polyurethane/polyurea polymer; and in some embodiments b) an adhesive layer. In some embodiments the layer additionally comprises a non-crosslinked polymer forming a semi-IPN with the crosslinked polymer. In some embodiments the non-crosslinked polymer may be selected from the group consisting of polyurethane, polyurea, and mixed polyurethane/polyurea polymer. In some embodiments the crosslinked polymer may additionally comprise an acrylate-containing component.

CROSS REFERENCE TO RELATED APPLICATION

This application is a divisional of U.S. application Ser. No.12/367,146, filed Feb. 6, 2009, now allowed, now U.S. Pat. No.8,916,271, which claims priority to U.S. Application No. 61/027,177,filed Feb. 8, 2008, the disclosures of which are incorporated byreference herein in their entirety.

FIELD OF THE DISCLOSURE

This invention relates to polyurethane or polyurea tapes and films whichinclude a semi-interpenetrating polymer network (semi-IPN) and their usein surface protection, including protection of aircraft surfaces fromerosion due to water and particles such as sand and dust.

SUMMARY OF THE INVENTION

Briefly, the present disclosure provides a film or tape comprising: a)at least one layer comprising a crosslinked polymer selected from thegroup consisting of crosslinked polyurethane, crosslinked polyurea, andcrosslinked mixed polyurethane/polyurea polymer; and b) an adhesivelayer. In some embodiments the layer additionally comprises anon-crosslinked polymer forming a semi-IPN with the crosslinked polymer.In some embodiments the non-crosslinked polymer may be selected from thegroup consisting of polyurethane, polyurea, and mixedpolyurethane/polyurea polymer. In some embodiments the crosslinkedpolymer may additionally comprise an acrylate-containing component.

In another aspect, the present disclosure provides a constructioncomprising a film or tape as provided herein bound by an adhesive layerto a surface of a composite part or metal part.

In another aspect, the present disclosure provides a composite partcomprising a resin matrix and an outer surface layer differing incomposition from the resin matrix, where the outer surface comprises atleast one layer comprising a crosslinked polymer selected from the groupconsisting of crosslinked polyurethane, crosslinked polyurea, andcrosslinked mixed polyurethane/polyurea polymer. In some embodiments thelayer additionally comprises a non-crosslinked polymer forming asemi-IPN with the crosslinked polymer. In some embodiments thenon-crosslinked polymer may be selected from the group consisting ofpolyurethane, polyurea, and mixed polyurethane/polyurea polymer. In someembodiments the crosslinked polymer may additionally comprise anacrylate-containing component.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a schematic of the apparatus used to test for rain erosionresistance, as described in the Examples and in U. S. Published PatentApp. No. 2008/0209981-A1, published on Sep. 4, 2008, the disclosure ofwhich is incorporated herein by reference.

FIG. 2 is a photograph of Example 1 film and Example 4C film(comparative) on a substrate prior to testing as described in theExamples.

FIG. 3 is a photograph of Example 1 film and Example 4C film(comparative) on a substrate after testing as described in the Examples.

DETAILED DESCRIPTION

The present disclosure provides polyurethane or polyurea tapes and filmswhich include a semi-interpenetrating polymer network (semi-IPN) andtheir use in surface protection, including protection of aircraftsurfaces from erosion due to water and particles such as sand and dust.Also covered is the ability to protect surfaces, not limited toaircraft, that are subjected to elevated temperatures in use or duringmanufacture. The crosslinked component of the semi-IPN may be comprisedof a urethane (or urea) acrylate oligomer that is crosslinked to form anetwork within the non-crosslinked component. The non-crosslinkedcomponent may be a thermoplastic polyurethane/polyurea, which ischemically distinct from the crosslinked component.

In some embodiments, protective tapes and films disclosed in thisinvention can be used to protect surfaces of aircraft including leadingedges of wings, radomes, and helicopter rotors from damage due to water,sand, dust, or debris. The semi-IPN polyurethane of the presentinvention can offer better erosion resistance than a thermoplasticpolyurethane alone. A tape with a pressure sensitive adhesive offers asimple way of applying the film to the aircraft and makes repairs easy.The film alone can withstand temperatures not possible withthermoplastic films, allowing the film to be co-cured into compositestructures. The extent of crosslinking of the polyurethane/polyurea canbe varied, allowing for a solvent resistant film or one that isremovable with solvents yet still has elevated temperature capabilities.A lower extent of crosslinking can also result in a film that hasintegrity at high temperatures, yet has the ability to be thermoformed.A higher extent of crosslinking can prevent thermoforming from beingpossible.

Protective films and tapes of this invention also have utility forprotecting non-aircraft surfaces that are subjected to heat either inservice or during the manufacturing process. Sporting good, automotive,tool, cooking or heating equipment and general industrial applicationsare potential avenues for this film or tape where either processingtemperatures or in-use temperatures are elevated and would require afilm that can withstand elevated temperatures.

The disclosures of the following references are incorporated herein byreference: U.S. patent application Ser. No. 11/837,293, filed Aug. 10,2007; U.S. Pat. No. 5,959,775; U.S. Pat. No. 4,948,859; U.S. Pat. No.4,859,742; and U.S. Pat. No. 4,302,553.

Some embodiments comprise a film or tape that comprises at least onelayer comprising a crosslinked polymer selected from the groupconsisting of crosslinked polyurethane, crosslinked polyurea, andcrosslinked mixed polyurethane/polyurea polymer and an adhesive layer.Any suitable crosslinked polyurethane or crosslinked polyurea may beused. Suitable polyurethanes may include polymers of polyisocyanates andpolyols. Suitable polyureas may include polymers of polyisocyanates andpolyamines. In some embodiments, the crosslinked polymer may be a mixedpolyurethane/polyurea polymer derived from polyisocyanates and a mixtureof polyols and polyamines. Any suitable polyisocyanates, polyols orpolyamines may be used. Suitable polyisocyanates may include aromaticisocyanates, aliphatic isocyanates, polyisocyanates, or combinationsthereof. Suitable aromatic isocyanates may include Methylene diphenyldiisocyanate, 1,4-Phenylene diisocyanate, 1,3-Phenylene diisocyanate,3,3′-Dimethyl diphenylmethane-4,4′-diisocyanate,Diphenylmethane-2,2′-diisocyanate, naphthalene diisocyanate,4,4′-Biphenyldiisocyanate, 1,5-Naphthalene Diisocyanate,2-Methyl-1,5-naphthalene diisocyanate, 2,4-toluene diisocyanate and2,6-toluene diisocyanate and mixtures of the two isomers,diphenylmethane-2,4′-diisocyanate, 4-Ethyl-m-phenylenediisocyanate, andthe like, or mixtures thereof. Suitable aliphatic isocyanates mayinclude 2,4,4-Trimethylhexamethylene diisocyanate,2,2,4-Trimethylhexamethylene diisocyanate, 1,4-Cyclohexane diisocyanate,1,3-cyclohexyl diisocyanate, Trimethylhexamethylene diisocyanate,Isophorone Diisocyanate (IPDI), Decamethylene diisocyanate, Methylenediisocyanate, Methylene-bis(4-Cyclohexylisocyanate) (H12MDI), dimethyldiisocyanate, trans-1,4-Cyclohexane diisocyanate, hexamethylenediisocyanate, and the like, or mixtures thereof. Other suitableisocyanates may include polyisocyanates, including those based on any ofthe above. Suitable polyols may include polyester polyols,polycaprolactone polyols, polyether polyols, hydroxyl terminatedpolybutadiene and hydrogenated polybutadiene polyols, polycarbonatepolyols, and the like, or mixtures thereof. Suitable polyamines mayinclude JEFFAMINE® polyetheramines and the like, or mixtures thereof. Inaddition, chain extenders may be included, which are typically monomericor low molecular weight difunctional compounds. Suitable hydroxy chainextenders may include ethylene glycol, diethylene glycol, propyleneglycol, dipropylene glycol, neopentyl glycol, 1,4 butanediol, and2-methyl-1,3-propylenediol and the like, or mixtures thereof. Suitableamino chain extenders may include 1,4 diaminobutane, Ethylenediamine,1,2 diaminopropane, 1,3 diaminopropane, 1,2 diaminocyclohexane,isophorone diamine, secondary cycloaliphatic diamines,diethyltoluenediamine, and the like, or mixtures thereof.

In some embodiments, the crosslinked polymer may additionally comprisean acrylate component. The acrylate component is derived from anysuitable acrylate component precursor, which is any suitable monomer,oligomer or polymer with an acrylate double bond available forpolymerization. In some embodiments, acrylate component precursors arecrosslinked by e-beam or other radiation during formation of the tape toform the acrylate component ultimately present in the finished tape.

In some embodiments, the acrylate component precursor is copolymerizedinto the polyurethane or polyurea prior to crosslinking of the acrylatecomponent precursor. Suitable acrylates of this type, such as SR495B,include one or more groups which polymerize with the polyurethane orpolyurea, such as alcohol or amine groups, and one or more acrylatedouble bonds available for polymerization. Other suitable species mayinclude caprolactone acrylates, hydroxyethyl acrylate, dipentaerythritolpentaacrylate, and the like, or mixtures thereof.

In some embodiments, the acrylate component precursor is blended withthe polyurethane or polyurea prior to crosslinking of the acrylatecomponent precursor. In this embodiment, the polyurethane or polyureaform a semi-interpenetrating polymer network with the crosslinkedacrylate component in the final tape. A semi-interpenetrating polymernetwork is formed where the acrylate-containing component is crosslinkedand the other polyurethane or polyurea is not. Suitable acrylates ofthis type include CN996, CN9893, and the like, including such acrylatesavailable from Sartomer. Suitable acrylates of this type are typicallyat least partially miscible in the polyurethane or polyurea.

The crosslinked polymer may be crosslinked by any suitable means,including radiation crosslinking, such as by e-beam, UV, visible light,IR, and the like, or covalent crosslinking achieved by the inclusion ofcrosslinking agents or polyfunctional monomers in the polymer duringmanufacture. Polyfunctional monomers may include polyisocyanates,polyols, polyamines, and the like, or mixtures thereof.

The tape or film is typically transparent or translucent but may also bepigmented. The tape may have any suitable thickness. Typical thicknessis between 0.01 mm and 3.0 mm, more typically between 0.01 mm and 1.0mm, more typically between 0.1 mm and 1.0 mm, more typically between0.25 mm and 1.0 mm, and more typically between 0.25 mm and 0.75 mm.

Any suitable adhesive layer may be used. In one embodiment, the adhesivelayer may comprise an acrylic adhesive. In one embodiment, the adhesiveis a pressure-sensitive adhesive. In one embodiment, the adhesive is astructural adhesive. In one embodiment, the adhesive is two-partadhesive. In one embodiment, the adhesive is a energy-cured adhesive. Inone embodiment, the adhesive is a air cured adhesive. Suitable adhesivesmay include acrylics, polyurethanes, silicones, styrene-butadiene blockcopolymers, styrene-isoprene block copolymers, epoxies, cyanoacrylates,two-part urethane, and the like.

The tape may be made by any suitable method, including thosedemonstrated in the Examples below. Suitable methods may includeblending of polyurethane or polyurea component with a crosslinkablecomponent, reactive extrusion or reactive coating.

The use of fiber reinforced resin matrix or fiber reinforced plastic(FRP) matrix composite laminates (“composites”) has become widelyaccepted for the variety of applications in aerospace, automotive andother transportation industries because their light weight, highstrength and stiffness. Weight reduction benefits and performanceenhancements are the biggest drivers behind implementation of fiberreinforced resin matrix composite laminates into industrialapplications. Various airspace components being manufactured fromfiberglass and carbon fibers reinforced composites including airplanefuselage sections and wing structures. Composites are used to fabricatemany parts for airplanes, wind generators, automobiles, sporting goods,furniture, buses, trucks, boats, train cars and other applications wherestiff, light-weight materials, or consolidation of parts are beneficial.Most often the fibers are made of carbon, glass, ceramic or aramid, andthe resin matrix is an organic thermosetting or thermoplastic material.These parts are typically manufactured under vacuum and/or pressure attemperatures from 0° C. to 180° C. and occasionally up to 230° C. Insome embodiments a film or tape according to the present disclosure maybe adhered to such a composite part.

In some embodiments a film or tape according to the present disclosuremay be use to line a mold used to form a part, such that after themolding process the resulting part has an outer surface of the film ortape. In some embodiments such a part is a composite part. Any suitablemolding process may be used, including molding of polymers, composites,fiberglass, and the like. The present disclosure includes a molded parthaving an outer layer which includes in whole or in part a film or tapeaccording to the present disclosure. The molded part may be of anysuitable molded material, including thermoplastic polymers, thermosetpolymers, curable polymers, composites, fiberglass, ceramics, clays, andthe like.

Objects and advantages of this invention are further illustrated by thefollowing examples, but the particular materials and amounts thereofrecited in these examples, as well as other conditions and details,should not be construed to unduly limit this invention.

EXAMPLES

The following Examples demonstrate manufacture of semi-IPN polyurethanetapes are made and demonstrate improved durability of these tapes over acomparable thermoplastic polyurethane tape. Two semi-IPN polyurethanetapes were made.

Unless otherwise noted, all reagents were obtained or are available fromAldrich Chemical Co., Milwaukee, Wis., or may be synthesized by knownmethods.

TABLE 1 Materials used in the examples Material Description PPT 86670.028″ thick Polyurethane Protective Tape with 0.003″ of acrylicadhesive available from 3M Company, St. Paul, MN. Color 36173 gray PPT8542 0.020″ thick black Polyurethane Protective Film, this iscommercially available in tape form with an acrylic adhesive from 3MCompany, St. Paul, MN Gray Pigment Gray pigmented polyurethane per FedStd 595 color 36173 Black Pigment Black pigmented polyurethaneKrystalgran Thermoplastic polyurethane available from HuntsmanPN3429-108 Corporation, The Woodlands, TX CN9893 Aliphatic UrethaneAcrylate Oligomer available from Sartomer Company, Exton, PA Pre-preg250° F. cure (121° C.) epoxy prepreg, Hexcel F155Film Extrusion

Film extrusion was performed on a 58 mm Davis Standard, co-rotating twinscrew extruder. It has a L/D ratio of approximately 84:1 and extrudesthrough a 26 inch wide die. The films were corona-treated with anon-line corona treatment apparatus.

The samples were cast onto a matte paper casting liner. The castingliner had a polyester tape adhered to the backside to prevent thepolyurethane from sticking to it and splitting the paper when unwound.Table 2 shows the component feed rates for the samples.

TABLE 2 Extrusion Rates Krystalgran PN3429-108 Pigment CN9893 Line RateSample (lb/hr) (lb/hr) (lb/hr) (ft/min) Example 1 Film 130.5 4.5 (gray)16.7 7.5 Example 2 Film 130.5 4.5 (black) 14.9 7.5

The polyurethane and pigments were fed separately by Ktron gravimetricfeeders. The CN9893 was fed from a heated pressure vessel. The pressurevessel held 15 gallons and was made of stainless steel. It was heated bywrapping with a heat blanket. The temperature of the heat blanket wasset to 170° F. The pot was pressurized to 60 psi with air and theflowrate was controlled manually with a needle valve. The pot was placedon a weigh scale, enabling consistent monitoring of the flowrate/weightloss.

The rolls were extruded to 26″ wide and 0.024″ thick. Approximately 200yards of each were collected.

E-Beam Treatment

The polyurethane rolls were ebeam irradiated. Due to the thickness ofthe films and the voltage limitation of the ebeam unit (260 kV max), thesamples were passed through the ebeam twice in order to irradiate thesamples from both sides. Table 3 summarizes the ebeam conditions for thesamples.

TABLE 3 Ebeam Conditions Dose Voltage Current Line Speed Sample (MRAD)(kV) (mA) (ft/min) Example 1 Film 16 260 75 100 Example 2 Film 16 260 75100

After ebeam exposure, the samples had become semi-IPN polyurethanes withthe acrylate forming a crosslinked network inside the thermoplasticpolyurethane. To validate this, all samples were heated to 300° F. for30 minutes and did not become glossy. If the network had not beenformed, the films would have become glossy. They were also all tested byplacing a strip in front of a heat gun. The samples did not melt,indicating the network had formed.

Coating with Adhesive

The samples were coated with a 90/10 isooctyl acrylate/acrylic acidmonomer mixture with photoinitiator at a coating thickness of 3 mil(0.076 mm), and then UV cured to form a pressure sensitive acrylicadhesive.

Rain Erosion Simulator

A schematic of the apparatus used to test for rain erosion resistance isshown in FIG. 1. This apparatus is outlined in detail in 3M patentfiling “METHOD OF TESTING LIQUID DROP IMPACT AND APPARATUS,” U.S. patentapplication Ser. No. 11/680,784 filed Mar. 1, 2007.

The testing apparatus of FIG. 1 was assembled using a 0.177 caliber airgun (“Drozd Air Gun”, European American Armory Corporation, Cocoa, Fla.)and ½ inch diameter polyvinyl chloride tube as the barrel section. 4.5mm Grade II acetate pellets (Engineering Laboratories, Inc, Oakland,N.J.) are propelled through use of the pellet gun which is connected toa tank of compressed nitrogen (Oxygen Service Company, St. Paul, Minn.)set at about 60 psi. Samples are continuously coated with a stream ofwater delivered through use of a water pump (Part No. 23609-170, VWR,West Chester, Pa.). Velocity of the pellets was measured with a CEDMillennium Chronograph, available from Competitive Edge Dynamics LLC,Orefield, Pa.

The samples were tested by cutting a circle with a 6.1 cm diameter and a2.2 cm diameter hole in the middle and adhering this to a round 304stainless steel plate having an outer diameter of 7.6 cm and a centralhole with a diameter of 0.35 cm. The samples were allowed to dwell onthe substrate for 24 hours before testing. The tests were conducted at ashot rate of 3 shots/sec. The test results are shown in Table 4.

TABLE 4 Simulated Rain Erosion Test Results Sample Average Velocity(ft/s) Average Shots to Failure Example 1 Film 361.7 371.3 Example 2Film 363.3 372.3 Comparative 361.5 245.0 Example 3C (PPT 8667)

As evident by a higher “Shots to Failure” the Example 1 and 2 films wereshown to be more durable than PPT 8667, Comparative Example 3C. TheExample 1 and 2 films were semi-IPN polyurethane, while the ComparativeExample 3C film (PPT 8667) was a thermoplastic polyurethane of the samethickness.

Co-Cure

This example shows the ability of a semi-IPN polyurethane to be able tobe co-cured into a composite structure. This enabled the film to beadhered into the composite without the need for pressure sensitiveadhesives. It is possible with a semi-IPN polyurethane because thecrosslinked network prevents the film from melting and flowing duringthe curing process.

The following procedure was used to demonstrate the ability to co-cureinto a composite at elevated temperatures. A 2.5 inch long aluminumairfoil coupon was used as a tool. On top of the tool was placed arelease liner. Stacked on top of the release liner were 8 layers ofpre-preg arranged in a 0°-90°-0° criss-cross configuration. The pre-preglayers were all cut into 2.5″×3.5″ squares. On top of the pre-preg wasplaced a 1.25″×3.5″ sample of Example 1 film with no adhesive (as madein the previous example) side by side with a 1.25″×3.5″ sample of PPT8542 (no adhesive), designated Example 4C. Another release liner wasplaced on top of the polyurethanes. The construct was placed on a vacuumtable and covered with a rubber mat. Vacuum was pulled on the construct,sucking the rubber mat to the composite. The vacuum table was heated to250° F. over the course of ten minutes. When the table reached 250° F.,it was held at that temperature for an additional 10 minutes. The heatwas turned off and vacuum remained on for an additional 5 minutes tohelp cool the table. After this, the composite was removed andinspected.

FIGS. 2 and 3 are photographs of the Example 1 and 4C films before andafter testing. The black Comparative Example 4C film became glossy asthe polyurethane melted. The melting of the Example 4C polyurethane alsocaused it to flow down as the vacuum sucked the rubber mat down andsqueezed the polyurethane towards the base. This left a thin layer ofthe Example 4C film on the top of the coupon and a thicker, wrinkledfilm towards the base. The Example 1 film became slightly more glossy,but still maintained its matte appearance. It molded to the compositewithout melting or flowing.

Various modifications and alterations of this invention will becomeapparent to those skilled in the art without departing from the scopeand principles of this invention, and it should be understood that thisinvention is not to be unduly limited to the illustrative embodimentsset forth hereinabove.

We claim:
 1. A method of making a part comprising the steps of: a)lining a mold with a film or tape which comprises asemi-interpenetrating network (semi-IPN) of: i) a crosslinked componentderived from a urethane acrylate and ii) a non-crosslinked componentwhich is a thermoplastic polyurethane; and b) performing a moldingprocess such that after the molding process the resulting part has anouter surface of the film or tape.
 2. The method according to claim 1wherein the molded part comprises a molded material selected from thegroup consisting of thermoplastic polymers, thermoset polymers, curablepolymers, composites, fiberglass, ceramics and clays.
 3. The methodaccording to claim 2 wherein the molded material is a resin matrixcomposite material.
 4. The method according to claim 2 wherein themolded material is a fiber reinforced resin matrix composite material.5. The method according to claim 1 wherein the molded part comprises amolded material and wherein the molding process comprises curing themolded material.
 6. The method according to claim 1 wherein the moldedpart comprises a molded material and wherein the molding processcomprises heat cure of the molded material.
 7. The method according toclaim 6 wherein the molded material is a resin matrix compositematerial.
 8. The method according to claim 6 wherein the molded materialis a fiber reinforced resin matrix composite material.
 9. The methodaccording to claim 1, wherein the urethane acrylate is at leastpartially miscible in the thermoplastic polyurethane.